EGFR and HER2–Akt–mTOR signaling pathways are activated in subgroups of salivary gland carcinomas

Abstract

Salivary gland carcinomas encompass a wide spectrum of histological entities. To identify candidate therapeutic targets and innovative treatment options for these carcinomas, we examined epidermal growth factor receptor (EGFR), phosphorylated EGFR (p-EGFR), HER2, and phosphorylated forms of Akt (p-Akt) and mammalian target of rapamycin (p-mTOR) in 47 salivary gland tumors using immunohistochemistry. EGFR overexpression was found in 51 % of the tumors (24/47); in particular, EGFR overexpression occurred in mucoepidermoid (seven out of seven) and salivary duct carcinomas (9/12). Although EGFR amplification was not detected by fluorescence in situ hybridization analysis, increased copy number due to polysomy of chromosome 7, which houses EGFR, was observed in 4 of the 24 tumors with EGFR overexpression; this polysomy occurred most frequently in salivary duct carcinomas (three out of nine). HER2 overexpression was observed in 21 % (10/47) of all tumors; in these 10 tumors, HER2 gene amplification was found in seven cases. p-Akt was found in 51 % (24/47) of all tumors, most frequently in mucoepidermoid carcinomas (six out of seven). p-mTOR was found in 57 % of the latter (four out of seven). Consequently, different signaling cascades were found activated: (1) an EGFR/HER2(-Akt)-mTOR-dependent axis, with gene gains of HER2 and/or EGFR, activated in salivary duct carcinoma and carcinoma ex pleomorphic adenoma; (2) an EGFR(-Akt)-mTOR-dependent pathway activated in mucoepidermoid carcinoma or acinic cell carcinoma, without HER2 or EGFR gene alterations; and (3) an Akt-dependent pathway without EGFR/HER2 activation in other types. These findings indicate that phosphoprotein mapping of components in the EGFR/HER2-Akt-mTOR pathways may be a useful guide to select appropriate targeting regimens.